1. Field of the Invention
The present invention relates to a turbo-molecular pump having rotor blades provided in multiple steps, stator blades provided between the rotor blades, and spacers for supporting the stator blades.
2. Description of the Related Art
In a turbo-molecular pump obtaining high vacuum or ultra high vacuum, a gas molecule suctioned from an intake port side is exhausted to an exhaust port side by a blade exhaust portion formed by rotor blades and stator blades. Frictional heat generated when the rotor blades rotated at high speed collide with the gas molecule is transmitted to a case member from the rotor blades via the stator blades.
When a temperature of a rotor having the rotor blades becomes high by the frictional heat, creep speed is accelerated. Thus, a cooling pipe is provided in the case member and a cooling medium is circulated in the cooling pipe, so as to cool the turbo-molecular pump.
In recent years, in manufacturing of a semiconductor device and the like, there is a tendency that a wafer is enlarged and a flow rate of a gas to be introduced into a process chamber is increased. When the flow rate of the gas is increased, the frictional heat in the rotor blades is increased, so that the temperature of the rotor becomes high. Therefore, only by providing the cooling pipe in the case member, the temperature of the rotor exceeds an allowable temperature and the creep speed is accelerated.